US20120170337A1 - Voltage multiplication in a wireless receiver - Google Patents

Abstract

A wireless energy transfer receiver includes an input configured to receive alternating current (AC) electric energy and an output configured to make available direct current (DC) electric energy. The receiver further includes a rectification component configured to convert the AC energy received at the input into DC energy available at the output, the DC energy made available as DC voltage; and a multiplication component configured to amplify a peak voltage of the AC energy received at the input, the DC voltage made available at the output correspondingly being higher than the peak voltage of the AC energy received at the input.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• The present application claims benefit to U.S. provisional application 61/428,139 filed Dec. 29, 2010 entitled Voltage Multiplication for Increasing the Charging Power Received at a Wireless Receiver, the contents of which is incorporated herein in its entirety.
BACKGROUND
• Energy transfer between two coupled inductors may occur through the use of a transmitter generating an oscillating magnetic field and a receiver converting the oscillating magnetic field into electric power. In many energy transfer systems the conversion is from oscillating magnetic field into a direct current (DC) voltage.
• The DC voltage is at least in part a function of magnetic field intensity and the coupling between the inductors. If the magnetic field intensity decreases or the coupling between the inductors decreases, then DC voltage may also decrease. If the DC voltage drops below the minimum voltage required by the load then energy transfer ceases.
BRIEF DESCRIPTION OF THE FIGURES
• FIG. 1 illustrates an exemplary wireless energy transfer system.
• FIG. 2 illustrates a representative exemplary implementation of a wireless energy transfer system.
• FIG. 3 illustrates another representative exemplary implementation of a wireless energy transfer system.
• FIG. 4 illustrates an exemplary circuit for voltage doubling.
• FIG. 5 illustrates another exemplary circuit for voltage doubling.
• FIG. 6 illustrates another exemplary circuit for voltage doubling.
• FIG. 7 illustrates another exemplary circuit for voltage doubling.
• FIG. 8A illustrates one exemplary wireless energy transfer system in which a voltage doubler rectifier is included in the receiver.
• FIG. 8B illustrates the effective circuit of an exemplary receiver including a voltage doubler rectifier when a voltage source is in a negative phase of its cycle.
• FIG. 8C illustrates the effective circuit of an exemplary receiver including a voltage doubler rectifier when a voltage source is in a positive phase of its cycle.
• FIG. 9A illustrates an exemplary implementation of a receiver which adaptively enables and disables a voltage multiplication component of a voltage multiplier rectifier circuit.
• FIG. 9B illustrates an exemplary implementation of an adaptive receiver in a first mode.
• FIG. 9C illustrates an exemplary implementation of an adaptive receiver in a second mode.
• FIG. 10 illustrates another exemplary implementation of a receiver with rectification multiplication circuitry.
• FIG. 11 illustrates an exemplary synchronous rectification circuit that may be used as a rectification multiplication circuit.
DETAILED DESCRIPTION
• A wireless energy transfer system may include coupled inductors or coils, a transmitter capable of generating a high-intensity oscillating magnetic field, and a receiver capable of converting the magnetic field into usable electric power. The electric power is provided to a load.
• The conversion of the magnetic field into usable electric power may include a rectification process if the load requires a continuous voltage source.
• In many systems the load requires a minimum voltage for proper operation. However, as the magnetic field intensity and/or the coupling between the inductors decreases, the voltage to the load may also decrease to a value below the minimum operational voltage of the load. It would be beneficial in some circumstances to have the capability on the receiver side to increase the voltage to the load so that the voltage to the load exceeds the minimum operational voltage requirements of the load.
• Additionally, the capability on the receiver side to increase the voltage to the load would beneficially allow for the transmitter to at least one of (i) generate a lower intensity magnetic field, (ii) allow for lesser coupling between the coils, and (iii) design the receiver coil with fewer turns, therefore saving cost and reducing losses.
• FIG. 1 illustrates an exemplary wirelessenergy transfer system100 including atransmitter105, areceiver110, aload115, andcoils120 and125.Transmitter105 provides a magnetic field atcoil120, which is magnetically coupled tocoil125.Receiver110 converts the magnetic field coupled oncoil125 to electric power provided to load115.
• Receiver110 includes aconversion component130, which further includes arectification component135 and amultiplication component140.Components130,135, and140 each represent at least one of or a combination of circuitry, firmware, and software that perform the underlying function of the respective component. Circuit elements ofrectification component135 and amultiplication component140 may be implemented within one circuit including within one integrated circuit or may be implemented within separate circuits.Receiver110 may include digital or analog circuits or a combination of digital and analog circuits.Components130,135, and140 are described further below.
• Receiver110 is connected to load115 at least viaconnections145 and150. Power provided toload115 is represented inFIG. 1 as a potential voltage difference Vout between a node ‘a’ onconnection145 and a node ‘b’ onconnection150.
• FIG. 2 illustrates a representative exemplary implementation of asystem100 in the form of a circuit diagram,system100 including atransmitter105, acoil120, acoil125, aconversion component130 withrectification component135, and aload115, as identified below the circuit diagram.
• Components oftransmitter105 include avoltage source205 and a transmitterresonant network210.Coil120 has self-inductance L1. A high-intensity oscillating magnetic field is established within transmitterresonant network210 andcoil120 by applyingvoltage source205 to transmitterresonant network210.
• The magnetic field is coupled to coil125 having self-inductance L2. The coupling coefficient betweencoils120 and125 is represented as ‘k’ on the circuit diagram.
• Coil125 is connected to areceiver resonator network220. As the magnetic field is coupled ontocoil125 it is converted into a high voltage oscillating signal withinreceiver resonator network220 andcoil125.
• Arectifier225 converts the oscillating signal into a direct current (DC) voltage. Acapacitor230 is used to reduce ripple in the DC voltage, and the DC voltage, Vout inFIG. 2, may be applied to a load.
• The circuitry illustrated inFIG. 2 is representative. Many other topologies are possible for implementingvoltage source205,resonator networks210 and220,rectifier225, andcapacitor230. Further, one or both ofcoils120 and125 may represent multiple coils.Coils120 and125 may be different sizes and shapes.Load115, although represented by resistance R, may be a complex load.
• FIG. 3 is a simplified equivalent of the circuit ofFIG. 2. The simplification is based on an assumption that the higher order harmonics of the square-wave voltage at the input of the rectifier are suppressed by the narrow-band filter formed by receiverresonant network220 andcoil125. Only the fundamental sinusoidal component is taken into account in determining an equivalent circuit. The assumption as stated allowsrectifier225,capacitor230, and load115 to be approximated by a resistor R_eq=R·8/π².
• Vout applied to the load is then described by equation (1), where ω is the operating frequency of the circuit expressed in radians per second (rad/s).
• 
  Vout_—eq(t)=Vout·4/π·sin(ωt)   (1)
• It can be shown that Vout is a strong function of the transmitter voltage source, such asvoltage source205 inFIG. 2. Vout can also be shown to be a strong function of the coupling betweencoils120 and125, for example as represented by coefficient k inFIG. 2. Thus, the amplitude of Vout varies with the amplitude of the magnetic field and the strength of the coil coupling.
• The magnetic field may be affected by the number and type of objects near the transmitter, the tuning of the resonant circuit, and the stability and efficiency of the voltage source, to name a few influencing factors. The coupling between the coils may be affected by distance between the coils, orientation of the coils with respect to each other, geometry of the coils, size difference between the coils, and the medium in the space between the coils (e.g., air, metal housing, and magnetic materials), to name a few influencing factors.
• As the magnetic field intensity decreases and/or the coupling between the coils weakens the magnitude of Vout decreases. When Vout drops below the minimum operational voltage required by the load, energy transfer ceases.
• Much research has been performed with the goal of increasing magnetic field intensity at the transmitter or increasing coupling between the coils of the transmitter and receiver. However, many influences affect magnetic field intensity and coupling in an actual user environment. Thus, even for a system in which the transmitter is designed to ideally generate a high intensity magnetic field and the system is designed to ideally achieve a strong coupling between the coils, the actual energy transfer predicted by the ideal design may not occur.
• As can be seen, there are many ways in which even a well-designed system may not effectively transfer energy to the receiver.
• It would therefore be desirable to provide for a multiplication of the voltage at the receiver. Not only would voltage multiplication at the receiver allow the system to perform effectively in an actual environment but also may allow the design requirements of the system to be relaxed, and may further allow the performance of the system to be improved with little or no change to the transmitter.
• A receiver including voltage multiplication may allow, for example, a lower transmitter source voltage, a greater distance between transmitter and receiver, and misalignment of the transmitting and receiving devices. Additionally or alternatively, because multiplication of the voltage at the receiver allows for weaker coupling between the coils, the coils may be smaller and/or may be designed using less costly material.
• Having identified the need for and benefit of voltage multiplication at the receiver, a suitable multiplier is selected. Referring again toFIG. 1,conversion component130 may includerectification component135 andmultiplication component140. As mentioned above,rectification component135 andmultiplication component140 may be implemented within one circuit and may share circuit elements, or may be implemented separately. Combination voltage multiplier and rectifier circuits may allow for a reduced overall circuit element count, which in turn may allow for reduced size and/or cost. Representative examples of combination voltage multiplier and rectification circuits are illustrated inFIGS. 4-7.
• FIG. 4 illustrates an exemplary Villard circuit. A Villard circuit is a voltage doubler circuit with rectification. The capacitor in the circuit ofFIG. 4 may also be used as resonant capacitor for the receiver coil, effectively limiting the rectifier to a simple diode. In the Villard circuit, the capacitor charges during negative phases of the coil voltage to the peak voltage of the negative phase. Effectively, the capacitor voltage provides a direct current (DC) offset for the coil voltage approximately equal to the absolute value of the peak voltage of the negative phase. The output voltage Vout of a Villard circuit oscillates between zero and roughly double the positive peak coil voltage.
• Large voltage swings at Vout such as from a Villard circuit may be difficult or impossible for a load to manage. There are a number of voltage multiplier circuits that reduce or minimize voltage ripple by using additional components. Illustrative examples are provided inFIGS. 5-7.
• FIG. 5 illustrates an exemplary Greinacher circuit for voltage doubling, described below.
• FIG. 6 illustrates an exemplary Delon voltage doubler circuit. One capacitor is charged during negative cycle phases and one capacitor is charged during positive cycle phases, each capacitor charged to the peak value of its respective phase. Vout is the sum of the voltages on the two capacitors, roughly the positive phase peak voltage plus the absolute value of the negative phase peak voltage.
• FIG. 7 illustrates another exemplary voltage doubler circuit, similar to the circuit ofFIG. 6 but with a split coil. Both capacitors are charged during both phases, reducing the ripple on the output voltage Vout.
• Many other circuit topologies may be implemented to multiply the voltage applied at Vout, not limited to voltage doublers. Further, multipliers may be cascaded. Different circuit topologies may include different filtering mechanisms to shape the voltage at Vout as desired.
• FIG. 8A illustrates one exemplary wireless energy transfer system in which a Greinachervoltage doubler rectifier805 as illustrated inFIG. 5 is included in the receiver.FIGS. 8B and 8C provide a simplified explanation of the voltage doubling function of the Greinacher circuit.
• FIG. 8B illustrates the voltage across the receiver coil as a voltage source Vin that is in a negative phase of its cycle with peak voltage −Vp. Current flows intoreceiver110 as shown byarrow810.Diode815 is forward biased and begins to conduct, and develops a forward bias voltage Vd.Capacitor820 is charged from the current flowing throughdiode815 to a voltage of amplitude Vp−Vd, biased as shown inFIG. 8B. Near the end of the negative phase of thecycle diode815 stops conducting, leavingcapacitor820 charged to Vp−Vd. Reciever coil voltage Vin then transitions to a positive phase of its cycle as illustrated inFIG. 8C.
• FIG. 8C illustrates Vin as positive, which establishes a forward bias ondiode830 so thatdiode830 begins to conduct and develops a forward bias voltage Vd as shown. Current flows as illustrated byarrow835.Capacitor840 begins to charge from the series connection of coil voltage Vin andcapacitor820 which still is charged to approximately Vp−Vd. In the simple case where the peak negative and positive voltages of Vin are equal,capacitor840 charges to a maximum voltage of (Vp+(Vp−Vd)−Vd)=2Vp−2Vd. In thisway capacitor840 is charged to roughly double the peak input voltage. Thecapacitor840 voltage is Vout provided to the load.
• Although the Greinacher circuit implementation is illustrated and described in detail, other voltage multipliers or multiplier/rectifiers may be used instead.
• The use of voltage multiplier circuits allowsreceiver110 to be placed at greater distances before the load voltage drops below usable voltage levels. However, when a voltage-multipliedreceiver110 is then placed closer to atransmitter105 thereceiver110 circuitry may be subjected to higher voltage stresses. In such a situation it is possible that the voltage on a circuit element may exceed the element's voltage rating, causing the element and thusreceiver110 to operate undesirably. To avoid thiscircumstance receiver110 may be designed to withstand high voltages. However, high voltage designs may be cost, size, or otherwise prohibitive.
• It would therefore be advantageous to have the capability to enable voltage multiplication atreceiver110 only when needed, or conversely to disable voltage multiplication atreceiver110 when close to atransmitter105. Thereceiver110 circuitry may then be designed for lower voltages.
• FIG. 9A illustrates an exemplary implementation of areceiver110 which adaptively enables and disables avoltage multiplication component140 of a voltage multiplier rectifier circuit. In the example ofFIG. 9receiver110 includes aswitching circuit905 with aswitch910 andcontroller915.Switch910 may be any semiconductor or other switching device and is illustrated as a field effect transistor (FET) merely for convenience. Acontroller915 monitors the voltage at a point within the receiver, and turnsswitch910 on or off according to the monitored voltage, as described below.Controller915 may include hysteresis such that the voltage must cross a first voltage threshold forcontroller915 to turnswitch915 on, and must cross a second threshold forcontroller915 to turnswitch915 off.
• Monitoring of the voltage may be performed by a separate circuit outside of thereceiver110 circuitry. For example, in a smart phone there may be a voltage monitoring circuit that monitors voltages at various locations within the circuitry of the smart phone, and one such monitoring location may be atreceiver110. In the smart phone example, a processor may evaluate the voltage measurements made by the monitoring circuit and provide signals according to the evaluation. One such signal may be an indication provided tocontroller915 to turnswitch910 on or off. Other implementations are also possible. For example,controller915 may be one circuit on areceiver110 integrated circuit chip that performs voltage monitoring and controls switch910.
• The receiver ofFIG. 9A further includesdiodes920,925,930, and935, andcapacitors940 and945. These circuit elements are discussed with respect toFIGS. 9B and 9C.
• FIG. 9B represents the receiver ofFIG. 9A whenswitch910 is turned on. Withswitch910 on,diode930 is short-circuited.Diode925 is not used for rectification or multiplication whenswitch910 is turned on. The effective rectification multiplication circuit includes onlydiodes920 and935 andcapacitors940 and945, and is recognizable as a Greinacher circuit that roughly doubles the peak input voltage as discussed above.
• FIG. 9C represents the receiver ofFIG. 9A whenswitch910 is turned off. Withswitch910 off,receiver110 provides rectification with no multiplication. When the voltage across the receiver coil is in a negative phase,diodes925 and935 conduct, chargingcapacitor945 to some voltage less than the absolute value of the receiver coil negative peak voltage. When the voltage across the receiver coil is in a positive phase,diodes920 and930 conduct, chargingcapacitor945 to some voltage less than the receiver coil positive peak voltage. The voltage oncapacitor945 depends at least in part on the ratio of the capacitance ofcapacitors940 and945.
• In some implementations, an active rectifier topology is used such that, for example, metal oxide semiconductor FETs (MOSFETs) may be used to replace one or more ofdiodes920,925,935, and930. In such implementations the adaptive multiplication may be implemented with potentially no additional cost.
• FIG. 10 illustrates another exemplary implementation of areceiver110 with rectification multiplication circuitry. In this example,receiver110 includes a rectification circuit as described above with respect toFIG. 9C and also includes a switch1005 (Qaux) that provides the multiplication function.
• Withoutswitch1005,receiver110 is a rectifier as described above. Whenswitch1005 is closed, the receiver coil andcapacitor1010 form a resonant tank circuit. The quality factor of this resonant tank is very high and after a few cycles a large amount of energy is stored in the resonant tank. During thetime switch1005 is closedcapacitor1015 delivers power to the load.
• Whenswitch1005 is opened from a closed position the energy stored in the resonant tank gets transferred tocapacitor1015. Thus, the voltage acrosscapacitor1015, load voltage Vout, increases.
• The switching frequency ofswitch1005 may be independent of the resonant frequency of the transmitter and receiver circuits and may be chosen to achieve a certain regulation accuracy and output voltage ripple.
• To minimize switching losses,switch1005 may be, for example, switched on at zero voltage and off at zero current.
• FIG. 11 illustrates an exemplary synchronous rectification circuit that may be used as a rectification multiplication circuit similar to the circuit ofFIG. 10.Receiver110 inFIG. 11 includesswitches1105,1110,1115, and1120, one switch for each diode in a full wave rectifier. In this manner, the voltage drop across the diodes in forward bias mode is eliminated.
• In the synchronous rectification circuit ofFIG. 11, ifswitches1115 and1120 are closed (shorting diodes Q2 and Q4, respectively) then the effective circuit is substantially similar to the circuit ofFIG. 10 withswitch1005 closed. The circuit ofFIG. 11 may operate in a voltage multiplication mode by closingswitches1115 and1120 (or switches1105 and1110) to charge the resonant tank, then openingswitches1115 and1120 (or switches1105 and1110) tocharge capacitor1130. Whilecapacitor1130 is charging, synchronous operation ofswitches1105,1110,1115, and1120 may occur as described above. Thus, the synchronous rectification circuit ofFIG. 11 may also be used to provide for multiplication with little or no additional cost.
• An active rectifier topology may be used such for one or more of the circuits described above. For example, metal oxide semiconductor FETs (MOSFETs) may be used to replace one or more diodes.
CONCLUSION
• A receiver has been described that improves wireless energy transfer by providing the capability of multiplication of the receiver coil voltage. Such a receiver provides improved performance and may reduce the price of wireless energy transfer systems. The multiplication capability of the receiver may be adaptively turned on and off. A plurality of exemplary implementations has been provided to illustrate a few of the possible topologies that enable multiplication within the receiver.
• The above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the technologies discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation.
• All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.

Claims (21)

1. An apparatus configured for inclusion in a wireless energy transfer receiver in an electronic device comprising:

an input configured to receive alternating current (AC) electric energy;

an output configured to make available direct current (DC) electric energy;

a rectification component configured to convert the AC energy received at the input into DC energy available at the output, the DC energy made available as DC voltage; and

a multiplication component configured to amplify a peak voltage of the AC energy received at the input, the DC voltage made available at the output correspondingly being a multiple of the peak voltage of the AC energy received at the input.

2. The apparatus ofclaim 1, the rectification component and the multiplication component being implemented in separate circuits.

3. The apparatus ofclaim 1, the rectification component and the multiplication component being implemented in one circuit.

4. The apparatus ofclaim 3, implemented in an integrated circuit.

5. The apparatus ofclaim 3, the input comprising a first terminal and a second terminal, the one circuit including

a first capacitor, a first end of the first capacitor electrically connected to the first terminal;

a first diode, the first diode cathode electrically connected to a second end of the first capacitor, the first diode anode electrically connected to the second terminal;

a second diode, the second diode anode electrically connected to the first diode cathode and to the second end of the first capacitor; and

a second capacitor, a first end of the second capacitor electrically connected to the second diode cathode, a second end of the second capacitor electrically connected to the second terminal, wherein the potential difference across the second capacitor is the DC voltage available at the output.

6. The apparatus ofclaim 5, implemented in an integrated circuit.

7. The apparatus ofclaim 3, the input comprising a first terminal and a second terminal, the one circuit including

a first capacitor, a first end of the first capacitor electrically connected to the first terminal;

a first diode, the first diode anode electrically connected to a second end of the first capacitor, the first diode cathode electrically connected to a first circuit node;

a second diode, the second diode anode electrically connected to a second circuit node, the second diode cathode electrically connected to the first diode anode and to the second end of the first capacitor;

a third diode, the third diode anode electrically connected to the second terminal, the third diode cathode electrically connected to the first circuit node;

a fourth diode, the fourth diode anode electrically connected to the second circuit node, the fourth diode cathode electrically connected to the third diode anode and to the second terminal; and

a second capacitor, a first end of the second capacitor electrically connected to the first circuit node, a second end of the second capacitor electrically connected to the second circuit node, wherein the potential difference across the second capacitor is the DC voltage available at the output.

8. The apparatus ofclaim 7, further comprising:

a switch that when closed implements a short circuit across the fourth diode; and

a controller that controls the switch.

9. The apparatus ofclaim 8, the switch being turned on at receiver power-up, the controller monitoring the first circuit node voltage, the controller causing the switch to turn off when the first circuit node voltage exceeds a threshold.

10. The apparatus ofclaim 8, the switch being turned off at receiver power-up, the controller monitoring the first circuit node voltage, the controller causing the switch to turn on when the first circuit node voltage does not exceed a threshold.

11. The apparatus ofclaim 8, the switch being a field effect transistor (FET).

12. The apparatus ofclaim 8, the first, second, third, and fourth diodes being implemented with field effect transistors (FETs).

13. The apparatus ofclaim 12, the fourth diode and the switch being implemented together with one FET.

14. The apparatus ofclaim 8, implemented in an integrated circuit.

15. The apparatus ofclaim 7, further comprising:

a switch that when closed implements a short circuit between the second terminal and the second end of the first capacitor.

16. The apparatus ofclaim 7, further comprising:

a first switch that when closed implements a short circuit across the first diode;

a second switch that when closed implements a short circuit across the second diode;

a third switch that when closed implements a short circuit across the third diode; and

a fourth switch that when closed implements a short circuit across the fourth diode;

wherein in a first mode the first, second, third, and fourth switches are synchronized with voltage received at the input such that each switch is closed when the corresponding diode is forward biased and each switch is opened when the corresponding diode is reverse biased; and

wherein in a second mode the second switch and fourth switch are closed such that a short circuit is effectively formed between the second terminal and the second end of the first capacitor.

17. The apparatus ofclaim 16, implemented in an integrated circuit.

18. A wireless energy transfer receiver in an electronic device, comprising:

a coil; and

a circuit electrically connected to the coil, the circuit configured to receive electrical energy inductively coupled onto the coil and to make energy available at an output, the circuit including

a rectification component configured to convert alternating current (AC) electric energy coupled onto the coil into direct current (DC) electric energy made available as DC voltage at the output; and

a multiplication component configured to amplify a peak voltage of the AC energy coupled onto the coil, the DC voltage made available to the load correspondingly being a multiple of the peak voltage of the AC energy.

19. The wireless energy transfer receiver ofclaim 18, the circuit implemented in an integrated circuit.

20. The wireless energy transfer receiver ofclaim 18, implemented in an integrated circuit.

21. A method, comprising:

receiving alternating current (AC) electric energy through inductive coupling in a wireless energy transfer receiver of an electronic device;

converting the AC electric energy into direct current (DC) electric energy in the form of DC voltage;

amplifying a peak voltage of the AC energy, the DC voltage correspondingly being a multiple of the peak voltage of the AC energy; and

providing the DC voltage at an output.

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